Recent technological developments are expected to establish the automated closed-loop control of physiological variables as a powerful tool for physiological research and clinical therapy. The objective of this project is to gain a basic understanding of applying modern control theory to the characterization and manipulation of physiological systems by considering the automated control of arterial blood pressure using infusion of vasoactive agents in chronically catheterized dogs. The specific goals for the current year: a) characterization of the response of blood pressure and total peripheral resistance to the infusion rate of vasoactive agents (nitroprusside, phenylephrine), b) determination of how the response varies with the operating point, and c) development and initial testing of optimal-control algorithms based on stochastic-control theory.